The present invention relates to a pneumatic radial tire for heavy loads, and more particularly to an improvement upon tread reinforcement to prevent structural failure and to diminish uneven wear of the tread.
In general, for pneumatic radial tires used for heavy loads for trucks and buses, there has been widely used the so-called steel radial ply tire. Such a tire comprises a carcass of radially arranged steel cords with the ends turned up around bead cores and a belt composed of 3 or 5 belt plies arranged on the crown of the carcass. Structural failure of the carcass and that of the bead was greatly decreased by improvement upon the carcass and bead structures, and the tires became used under more severe conditions such as higher speed and heavier loads.
Accordingly, with tires for heavy loads used under such conditions, inasmuch as its ground contacting pressure is much higher than that of passenger care tires, the so-called shoulder wear--uneven wear in which the edge part of the tread is greatly worn by slip against the road surface--is liable to be caused by the uneven rigidity of the tread and also by the difference between the diameters of the central part and the edge part of the tread.
Furthermore, due to the heat and strain generated by the tire rotation, the so-called tread separation--structural damage caused by an adhesive failure between the belt cords and rubber expanding from the belt ends of the third belt ply--is liable to result.